BMW legacy motors

I bought a bmw 118i 2016 model in jan 2021 from bmw legacy motors. I hardly drove the car as I work from home,2022 June it started cranking before it could start. I thought it was battery Issue, finally same year in November it gave in and car could not start, insurance towed the car back to the dealer and they gave me run arounds with diagnostic information. They only disclosed this year around March that it knocked the engine, and they not liable to fix it. As i demanded further explanation They told me it was a trade in from customer and it was modified "(not within bmw standards)" pervious owner had changed software and they had the audacity to sell such a car. Now they don't want to fix the car and they advising me to replace and engine on a car that I owned for less than 18 months. I would advise people to be very careful with this dealer better yet NOT associate themselves with it! they ************* in their dealings. The sales man Thabo was aware of the mechanical issues of the car, hence it was not even in the show room